Methods for detecting presence and measuring the concentration of minor overlapped components in gas chromatography

ABSTRACT

Gas chromatography is disclosed in which the signal (FIGS. 2 and 3 derived from the resulting gas emitted by the absorbent column is evaluated by a digital computer (41 FIG. 1). Minor components of gas associated with a major component are detected by observing a difference between the area on one side of a major peak or maximum of a curve or time function corresponding to the major component and the area on the other side of the peak (FIGS. 5; 6a, 6b). The evaluation also includes determination of the number of points of inflexion (FIGS. 6a, 6b) on each side of a major peak of a curve, one or no points on one side and two on the other (FIGS. 6a, 6b) indicates a minor component. Chromatographic apparatus is disclosed in which the recorders 51 are isolated from the gas measuring cell 23 and receive the signal to be recorded directly from the computer 41.

Elite Stts Pent Putnam et a1.

[451 Ar. in, 1973 1541 METHODS son DETECG 1 ASG [75] Inventors: RichardE. 1.1.11 Richard M. Au-

gusty, both of Pittsburgh, Pa.

[73] Assignee: a: house Elem 21c Coration,

Pittsburgh, Pa.

[22] Filed: July 25, 1968 [21] Appl. No.: 747,666

[52] US. Cl ..73/23.l [51] Int. Cl. ..G01n 31/08 [58] Field of Search73/23.1-27; 23/232 C; 55/67, 197, 386

[56] References Cited UNITED STATES PATENTS 3,069,895 12/1962 Burk ..7323.1 3,365,931 1/1968 MacRitchie ..73/23.l 3,412,241 11/1968 Spence..73/23.l X

OTHER PUBLICATIONS Computer Controlled Chromatographs-P. P.

Briggs-Control Engineering, Volume 14, No. 9, September 1967.

Gas Chromatography A. I. M. Keulemans-Reinhold Publishing Corporation,New York, 1957, pp. 36-39. Analytical Methods R. L. Pecsok Principlesand Practice of Gas Chromatography, John Wiley and Sons, Inc. New York,1959, pp. 145-150.

Primary ExaminerRichard C. Queisser Assistant Examiner-C. E. Snee, IIIAttorneyF. H. Henson and R. G. Brodahl STRACT Gas chromatography isdisclosed in which the signal (FIGS. 2 and 3 derived from the resultinggas emitted by the absorbent column is evaluate-:1 by a digital computer(41 FIG. 1). Minor components of gas associated with a major componentare detected by observing a difference between the area on one side of amajor peak or maximum of a curve or time function corresponding to themajor component and the area on the other side of the peak (FIGS. 5; 6a,6b). The evaluation also includes determination of the number of pointsof inflexion (FIGS. 60, 6b) on each side of a major peak of a curve, oneor no points on one side and two on the other (FIGS. 60, 6b) indicates aminor component. Chromatographic apparatus is disclosed in which therecorders 51 are isolated from the gas measuring cell 23 and receive thesignal to be recorded directly from the computer 41.

5 Claims, 15 Drawing Figures 51 RE -TO OTHER RECORDERS SPECIMAN GASPATENTEDAFRIOIUYZ 3, 2 ,127

sum 3 OF 3 VOLTS VOLTS TIME METHODS FOR DETECTENG PRESENCE AND MEASURINGTHE CONCENTRATHON OF MINOR OVERLAPPED COMPONENTS IN GAS CHROMATOGRAPHYBACKGROUND OF THE INVENTION This invention relates to the art ofdetection and measurement and has particular relationship to gaschromatography. Gas chromatography is a gas measurement andidentification process based on the property of certain substances ormedia to absorb gases or vapors in selectively different quantities.Typical media are kaolin, Celite (545) and diatomaceous earth fire brick(Johns-Manville C-22), in granular form (60 to 80 mesh) impregnated witha liquid, typically diisodecylphthalate, or 2,3-dimethylbutane and 3-methylpentane. Typically the ratio of liquid to solid by weight is 40 to100. Such a medium has different gassaturation volumes for differentgases.

When a specimen of a gas is passed through this medium each component ofthe specimen is absorbed until the medium is saturated by it. It thenproceeds along the column until the resulting quantity of a component isemitted by the medium. Each component is emitted from the medium at atime interval, after the specimen enters the medium, whose duration isdependent on the saturation-capacity of the medium for this component.The gaseous compounds in the medium are thus presented as a series ofrounded or peaked pulses whose time of occurrence and duration is afunction of the composition of the specimen. Typical gases to which thisphenomenon is applicable are the hydrocarbon products of a petroleumcracking plant and chromatography has been applied to theidentification, and determination of the relative quantities, of theproducts of such a plant. (See Gas Chromatography beginning page 290-316Analytical Chemistry, Volume 28, No. 3, Mar. 1956; articles MartinDimbat et al. 290-297, Fredericks et al. 297-303, Eggertsen et al303-306, McLafferty 306-316). A cracking plant can be effectivelymonitored and operated if effective and reliable facilities areavailable for evaluating the chromatographic pulses or curves of such aplant and it is an object of this invention to provide such facilities.

In gas chromatography a measured specimen of the gas or vapor underobservation is transmitted through the absorbing medium and theresulting gas emitted by the medium is transmitted through measuringmeans. The measuring means is connected to a recorder which produces achromatogram; that is, a graph including a plurality of individualcurves, each curve corresponding to one or more components of thespecimen gas. The composition of the specimen can be determined bycomparing the chromatogram produced for any specimen with a previouslyproduced chromatogram for a known specimen.

In this application the overall time-signal produced by a specimen willbe referred to as a chromatograph and the tracing of this signal on thetape of a recorder as a chromatogram. At the output of the cell thissignal is measured in volts (usually millivolts) as a function of time.The individual lobes of a. chromatograph, which correspond to componentsor compounds of the specimen will be referred to as time-functions,lobes, pulses or curves and the maxima points of thesetime-functions-there may be more than one-as maximum points or peaks.The envelope of each time-function is defined as the area embraced bythe time-function and the base line. These envelopes may have single,double or multiple peaks. The time of occurrence of a curve or timefunctions helps to identify the corresponding component of the specimenand the area of each curve or, less accurately, the maximum height orpeak of the curve, is a measure of the relative volumetric quantity ofthis component.

In accordance with the teachings of the prior art, (see articles above)gas chromatography is practiced by measuring the areas of the curves ofthe chromatograms with a planimeter or by producing templates of thecurves and weighing them. This procedure has the disadvantage that it istime-consuming and costly in labor and does not avail the curveevaluation promptly. In addition this procedure is not reliable wherethe pulses or curves overlap. Attempts have been made to overcome thelast-mentioned difficulty by attempting to find high resolution mediaand also by providing absorbing channels of great length and of smalldiameter. But the availability of high resolution media is limited andlong absorption channels of small diameter present serious problems inthe transmission of the gas or vapor under test.

In addition the process of deriving the curves from the measuring meansis confused, and the precision of the curves reduced, by the excessivenoise which appears on the chromatograms produced by the recorder. Thisnoise introduces difficulties in identifying components of the specimenswhich are of low magnitude.

It is an object of this invention to overcome the above-describeddifficulties and disadvantages and to provide a method of chromatographyand chromatographic apparatus which shall avail reliable and precisedata as to the composition of the gases under observation.

SUMMARY OF THE INVENTION In accordance with this invention an automaticchromatographic method and automatic chromatographic apparatus areprovided in which the output of the measuring means is evaluated by acomputer which determines in detail and precisely and reliably thecharacter of each component in the gas specimen. The electrical signalfrom the measuring means is converted into digital magnitudes and fed tothe computer. A succession of time-functions are thus available forevaluation by the computer. The computer measures the half areas of thetime functions and determines the number of points of inflexion of thesefunctions and from this data yields the required information on thecomposition of the specimen.

The aspect of this invention involving the recording of chromatogramsarises from the discovery that excessive noise in the output of themeaasuring means is produced by feedback from the recorder. Inaccordance with this invention the recorder is isolated from themeasuring means and is supplied from the computer with the signal to berecorded. For the eventuality that the computer is disabled, or forother purposes, a selector switch may be provided to connect the outputof the cell directly to the recorder.

To facilitate the understanding of the detailed description of thisinvention, it is desirable that the phenomenon of chromatography bedescribed in detail and some of its concepts additionally defined. Inchromatography according to this invention a succession of timefunctions each having a maximum are produced. The area under thetime-functions is proportional to the volumetric amounts of the variouscompounds or components present in the specimen. It is a principle ofchromatography that the elasped time ratios of the appearance of thevarious peaks is a constant for any one method and absorbent mediumsince these ratios are a function of the isotherms of theabsorption-column liquid-solid phase and compounds. The isotherms aregraphs in which is plotted, for different temperatures as parameters,the absorption of each compound or component in the liquid phase of theabsorbing medium against the absorption in the gas phase of this medium.The constant time ratios referred to above are the ratios of the timeintervals, after the start of a chromatographic operation, of theoccurrence of one peak and the occurrence of another peak. If T1 is theinterval after the start of the occurrence of peak 1 and T2 is theinterval after start of the occurrence of peak 2, (T1 IT 2) is aconstant under the conditions given.

The base line is defined at the commencement of the test by the signallevel at the start of the test from which the first pulse rises. Thesignal level at the end of the test, when only carrier gas is flowing,determines the position of the base line at the end of the test. Withcertain samples the height of the base line at two other preselectedpoints can also be established as part of the data collection programfor a given method. From this data the slope of the base line may bedetermined for the two ends of the chromatograph together with the pointof intersection if the slopes should not be the same. A base line shiftis not always present but must be taken into account. It is caused by achange in cell characteristic, carrier gas flow, liquid phasedeterioration or a deliberately-imposed temperature rise to assistcompound separation.

Elapsed time for any time function is the time between the commencementof the test set by the operator pressing the start button, and theappearance of the time-function. Alternatively a selected peak may beused as a reference for elapsed time of other peaks. The elapsed time isdifferent for different compounds included in a given method. For thesame compound it varies from one method to another. The apparatus isinitially calibrated with standard specimen and during this initialcalibration, these elapsed times are established and stored in thememory core of the computer. At the end of the test on a productionspecimen, the new time-function positions are compared with thoseobtained during the initial calibration of the homologous specimens anda compensating factor calculated for the integrated areas. Preferably,one or two sharp time-functions are used as the basis for thiscalculation.

It is also desirable preliminarily to consider the waveforms of some ofthe pulses or time functions which are produced.

Linear chromatography occurs with compounds which have linear isotherms.The shapes of these functions appearing as chromatograms on the recorderchart can be closely approximated by a Gaussian distribution as afunction of time.

Non-linear chromatogaphs occur with compounds or components which havenon-linear isotherms. Their envelopes do not lend themselves tomathematical analysis but may be identified for the purpose of comparingwith a standard.

Ideal chromatography may be linear or non-linear and occurs when themaxima are clearly separated from each other and the envelopes of thepulses or time functions do not merge.

Non-ideal chromatography occurs when the maxima of two or more compoundsare so close together in time that their envelopes merge.

From a study of several different chromatograms corresponding to a givenmethod, it is possible to write a program which identifies the typicalshape of the envelope produced by a given compound.

In the practice of this invention the specimen is passed through thechromatographic medium and the measuring means and the followingfunctions are performed.

1. The data is gathered.

2. Each time-function is analyzed; its gross area determined and theform of its envelope analyzed to detect unexpected compounds and minorcompounds.

3. Correction, particularly in the area, is made for time-base changes.

4. Correction, particularly in the area, is made for base line drift.

BRIEF DESCRIPTION OF DRAWING For a better understanding of thisinvention, both as to its organization and as to its method ofoperation, together with additional objects and advantages thereofreference is made to the following description taken in connection withthe accompanying drawings, in which:

FIG. 1 is a diagrammatic view showing apparatus for practicing thisinvention and also showing a preferred embodiment of this invention;

FIGS. 2 and 3 show, with respect to different time basis, achromatograph which is evaluated in the practice of this invention; and

FIGS. 4a through 10 show various features of typical time functionsencountered in the practice of this invention.

DETAILED DESCRIPTION OF THE INENTION The apparatus shown in FIG. 1includes a chromatograph channel 21 which may contain any of theabsorbing media listed in the above-identified articles, or others, andmay have the length and take any form (helical, for example) describedin these articles. This apparatus also includes a measuring cell 23 formeasuring the gas flow emitted by the channel 21. The cell 21 maymeasure thermal conductivity of the gas similarly to the cell of theMartin et al. article. A carrier gas which may be such gases as helium,argon, or hydrogen or mixtures of these gases is supplied to the channel21 through a conductor or channel 25. A measured quantity 10 CC forexample) of the specimen gas is injected into the conductor 25 through aconductor 27 so that the carrier and the specimen enter the absorbentmedium in the channel 21.

The channel 25 passes through the cell 23 so that the thermalconductivity of the carrier gas is measured. The resulting gas emittedby the medium in channel 21 is also supplied to the cell 23 through aconductor or channel 29 so that its thermal conductivity may be comparedto the conductivity of the carrier gas.

Each component or compound of the specimen gas is absorbed by the mediumuntil the medium is saturated. Each such component then only flows afterit has saturated the medium and conductor 29 carries a succession ofcontrolled pulses corresponding to the composition of the specimen. Thecell 25 has an electrical output 31 which produces a succession ofelectrical voltage signals or time functions on a base line. The baseline may be set by initially transmitting through the conductor 29 onlythe carrier gas emitted by the channel 21.

The apparatus according to this invention includes an analogue scanner33 to which the output 31 is connected. This scanner 33 may be suppliedfrom other chromatograph assemblies or units similar to the one justdescribed through conductors 35, 37, etc. The scanner 33 scans theseconductors 31, 35, 37 and converts the signals on each in its turn intoa digital signal. Each chromatograph unit may be supplied with adifferent specimen. The apparatus includes a range setter 39 with whichthe range for each conductor 31, 35, 37 may be set so that each signalis automatically at its most convenient magnitude on being converted.

The apparatus also includes a computer 41 having an adequate memory core(not shown) to which are connected an input/output typewriter 43, a tapepunch 45 and a tape reader 47. The computer 41 may be observed andcontrolled by an operator from a console (not shown). The computer 41has impressed thereon the digital output of the scanner 33 and evaluatesthe time-functions received. The core carries the timefunctions of aplurality of calibration standard specima which may be compared with theoutput of the scanner for the corresponding specima under observation.The standard calibration time-functions may be produced on a tape andinserted in the core by the tape reader 47. The tape punch may produce atape of the evaluation of the computer 41. Such evaluation may alsoappear on the typewriter. Typically the evaluation includes relationshipbetween each time-function and the corresponding standard time function,area of time function, number and heights of peaks of time function andcomparison of number of points of inflexion on each side of each peak;

The apparatus also includes a plurality of recorders 51 corresponding tothe number of cells scanned by the scanner 33. The recorders 51 areisolated from the corresponding cells 23 but are supplied from thecomputer 41 through analogue output devices 53, one associated with eachrecorder 51, the signal being sealed in the computer to correspond tothe range desired on the recorders. In setting this range for therecorders the computer bases its computations on the range set by therange setter 39 and on the desired range for the computer. The recorderproduces chromatograms.

FIGS. 2 and 3 are graphs, in which voltage is plotted against time, oftypical signals produced in the practice of this invention. The baseline 61, which is set by flow only of the carrier gas both throughconductor 25 and conductor 29, slopes downwardly because base line driftexists. The lobes 63 are the time functions corresponding to thecomponents of the specimen. FIG. 3

is a plot for a specimen identical to that of FIG. 2 passed through anidentical medium, at the same temperature, but with the carrier gasflowing at a substantially higher rate so that the time base 61 iscontracted.

FIGS. 4a, 4b, 4c are graphs showing typical time functions encounteredin the practice of this invention. Voltage is plotted against time.These functions are labeled appropriately. FIG. 4a shows a Gaussianfunction. FIGS. 4b and 4c are non-symmetric functions which do not lendthemselves to analysis but their areas can be determined and they can becompared with corresponding calibration functions in the computer memoryfor a standard specimen.

FIG. 5 is a graph showing a single time function having a single peakbut at least two points of inflexion on the trailing slope. Theimportant time intervals with reference to the start of the timefunction (initial low slope) are shown in FIG. 5 and are as follows:

t interval to occurrence of peak.

t, interval to occurrence of center of gravity of function.

= interval from occurrence of center of gravity to end of trailing slopeof function.

t duration of function.

h height of peak.

For a given method and component having characteristically a non-linearbut normally ideal time function, it can be postulated that theproportional dimenions of the function will not change withconcentration, i.e., the ratios to each other of time to peak (t time tocenter of area (t time to end of chromatogram (t and height (h) willalways be the same.

From tests, the ratio (t /t can be determined for that component andstored in the memory core. When running a test, integration begins at t,and continues until t, which can be predicted from t,,. This area is nowstored and a new integration begins. This new integration ends at thebase linegll p) is an improper fraction if the larger area is to theright of the peak and a proper fraction if the larger area is to theleft of the peak.

If no minor components are present,the area under line t, should beequal to half the area under line 1 i.e., area under 1,, is equal toarea under l The volumetric quantity of a minor component is thedifference between the area under 1, and the area under t The volumetricquantity of major component is equal to twice the smaller of the areasunder t or 2.

FIGS. 6a and 61) show linear-nonideal time functions and are labeled toshow how the evaluation for these time functions is carried out.

FIGS. 7a'and 7b show nonideal multi-peak time functions. In this casethe volumetric quantity of each component corresponding to a peak isdetermined by measuring the area of the time function under the peaks oneach side of the broken line.

FIG. 8 is a graph of a part of a signal showing nonideal multi-peak timefunctions which are merged. In this case the areas under the peak aredefined by broken lines and the volumetric quantity of each component isdetermined by measuring the area of the function under each peak andbounded by the function on one side and a broken line or by brokenlines.

FIGS. 9a and 9b show nonideal-time functions with an additional sharppeak on the trailing edge of the function. In this case the volumetricquantity of the minor component is determined from the area only underthe peaked curve, rising from the trailing edge of the principalfunction. The area of the trapezium shown in broken lines is included inthe area corresponding to the main function. This area of the trapeziumis subtracted from the area under the peaked curve to arrive at thequantity of the minor component.

. per second and the range setter 39 is capable of setting five ranges,e.g., 5, 10, 25, 50 and 500 millivolts. Any range can be used at anytime with any point. The output from the converter 33 is a 14-bit binaryword and has an accuracy of i 0.2 percent of full scale at any range.

Where the recorders 51 are driven in parallel in the scanning of acorresponding number of cell outputs 31, automation is achieved bydriving analogue outputs (53) from the computer so that they have thesame percent of the current measuring range that the range setter 39 hasselected for each output 31. The recorder 51 thus always works at itsbest sensitivity, and gain changes can be advised by the final print-outon the typewriter.

It is contemplated that 15 chromatographs, in a typical laboratorycontaining instruments will be in operation at any one time. At a totalscanning range of 100 points per second, and a chromatograph scanningrate of five times per second, 75 of 100 time units thus are taken up bythe chromatograph scanning. The remaining 25 scans which are availableper second are used to scan the output of a mass spectrometer located inthe laboratory. The gain on any point can be selected so that thepresent output is not more than 80 percent of full scale. Theprogramming is arranged to automatically adjust gain to give the bestmeasurement accuracy and to avoid saturating the amplifier.

For the typical practice of this invention, 70 different methods wereset up to analyze all the various production samples presented to thelaboratory of a petroleum cracking plant. The methods have been selectedto give good time-function separation and therefore best possibleaccuracy in chromatograph analysis. Each method is associated with acertain instrument, a specified column and the same group of compounds,all or only some of which may be present in the specimen submitted fortest. Any time-functions produced by compounds not included in theappropriate group are integrated and only printed out as an area,without identification other than elapsed time value. The maximumduration of each method is established.

Initially the chromatograph is calibrated and the various factors storedin memory core. When analyzing production specima, the operator insertsvia the typewriter or operators console the following data:

1. Method number.

2. Sample point from which the specimen has been drawn.

3. Chromatograph number to be used for the analysis.

The operator then inserts the specimen, presses the start button and thecomputer commences to gather data until the termination of the test. Thedata is analzyed, corrected and printed out as complete test results,the computer and instrument then being set to accept the next specimen.

During the data gathering the scanning of the chromatograph commencesand the recorder receives the appropriate signal and the base line ismeasured and stored. The recorder chart starts when the start button isdepressed. Typically, latching relays are provided, which are latched bythe depressing start button and unlatched by the depressing stop buttonor a computer contact.

During the scanning of the chromatograh outputs, the computer calculatesfor each one the slope of the curve and the rate of change of slope. Assoon as the slope of the signal, regarded as a voltage at an output 31,exceeds 5 microvolts per second, integration commences; the point ofcommencement in time being noted. For any envelope integration isfinally stopped when the slope has fallen below 5 microvolts per second.This point in time is also noted. Envelopes may contain more than onepeak and this is determined from the rate of change of slope; that is,from points of inflexion. Areas are allocated to compounds according tothe rules (a) through (I) stated below.

(This use of the points of inflexion is warranted. In any linearenvelope there is one point of inflexion on each side of the peak. Inany nonlinear envelope there may be no points of inflexion on eitherside of the peak. Any bump or lobe on even a straight line is associatedwith at least two points of inflexion. By counting the number of pointsof inflexion up to and away from each peak, one can determine whether anenvelope identifies a pure compound or more than one compound.)

The computer 41 carries out computations separately for each side of acurve about the peak. It notes the number of points of inflexion up tothe peak and notes the position of the peak in time, and stores the areaof the part of the curve or time-function up to the peak. It then startsa new integration after the peak, noting the number of points ofinflexion on the downward slope and continues to integrate until theslope falls to 5 microvolts per second. This may occur at the base lineor occur at the bottom of a valley, if two peaks are close together.

Analysis of the various chromatographs, as shown in FIGS. 4a through 10,is carried out as follows:

a. If the envelope has no points of inflexion on either side of the peakor only one point of inflexion on each side of the peak (FIG. 4a), thetwo integrated areas are summed and stored; in this case the curve wasproduced by, and identifies, only one compound.

b. If the envelope has one point of inflexion on one side but two ormore points of inflexion on the other side of the peak (FIGS. 6a, 6b),the area on the side containing only one point of inflexion is doubledand stored as the area for the major compound. The area of the minorcompound identified by the envelope is calculated by adding the twoareas together on either side of the peak and subtracting the areacalculated for the major compound present. This net area for the minorcompound would then be stored.

0. With an envelope having none or one point of inflexion on the leadingslope, and one or none on the trailing slope but also a valley on thetrailing edge which lies above the base line (FIGS. 7a, 7b), the twoareas on either side of the valley are allocated to each major compound.

d. If a peak lies between two valleys (FIG. 8), the area correspondingto a component is that lying between the bottoms of the adjacent valleyson either side of the peak.

e. A sharp peak occurring on a trailing slope (FIGS. 9a, 9b) is revealedby a sudden reversal in slope (upwardly FIGS. 9a and 9b). The slopeimmediately prior to the reversal is stored together with the previouslycomputed area and a new integration begins. This second integrationstops when the slope has returned to the value previously stored.Another integration now begins and continues until the slope has fallento microvolts per second. From the area under the sharp peak issubtracted a trapezium (broken lines FIGS. 9a, 9b) having a time widthcorresponding to the interval between the instant when the first slopeis stored and the instant when the slope returns to the value of thefirst slope. The mean height of the trapezium is equal to the mean valueof the signal at these two instants.

This trapezium is subtracted from the area under the sharp peak (FIGS.9a, 9b) to give the net area of the sharp peak which is allocated to theminor component whose peak time occurs at that point. The trapezium isadded to the first integrated area and the last integrated area to givethe total area allocated to the main component.

f. A sharp peak on the leading edge (FIG. 10) is manifest by a slopewhich suddenly approaches infinity. The slope just prior to this suddenincrease in slope is stored, a new integration bgins and a similarprocedure to that described in (e) is followed to calculate the areas.

Having now calculated the area attributed to each component which hasbeen identified by the position of its time-function, a correction isapplied to compensate for changes in time ratio for standard and forbase line drift.

The slope of the base line is calculated from the heights of the baseline as measured at different points in the program (FIGS. 2 and 3).This data may now be combined with the interval between the instant whenthe slope initially has a value of 5 microvolt/second and the instantwhen the slope returned to that magnitude of 5 microvolts per second.The areas of the trapeziums (shaded FIG. 2) under the various areascontributed by the base line may then be calculated. These areas aresubtracted from the total area attributed to each component to give thenet areas. These net areas are multiplied by the ratio of calibrationintervals (for the standards) to actual intervals for selected markerpeaks. All areas are multiplied by this factor to compensate for changesin the column or gas flow. Compensation for time ratios is effected bymultiplying the computed area by the standard time interval) divided bythe actual time (interval).

Each area so compensated is then multiplied by the area factorcalculated for each component during the initial calibration so as toproduce the volume of the component present in the sample analyzed.Standard calculation procedures are now applied to obtain mol percent,weight percent, liquid volume percent and sample properties such asaverage molecular weight and net heating value. The results are printedout in tabular form. Typically, 50 separate tests are run by thelaboratory as a whole during each 24 hour period.

Typically, about 385 compounds are encountered. The following data isstored permanently in the memory core for these compounds.

I. Identification 2. Molecular weight 3. Specific Heat 4. Density Foreach of the methods set up in the typical practice of this invention thefollowing data is stored in the memory core for each component:

1. identification of component 2. Elapsed time from start to major peaksdetermined in standard calibration.

3. Area factor (e.g. time-secs./c.c.) calculated during standardcalibration.

4. Peak type (single, multiple, linear, ideal, etc.)

Typically, there are a total of 511 sets of component data spread overthe 70 different methods. For each of these methods, the maximum testrunning time is also stored in the core. The maximum number of testsrunning at any one time is typically 15.

While preferred embodiments of this invention have been disclosedherein, many modifications thereof are feasible. This invention shouldnot be restricted except insofar as is necessitated by the spirit of theprior art.

We claim as our invention:

1. The method of determining the major components of the composition ofa specimen of a gas and the minor components, if any, associated witheach major component, the said method comprising passing said specimen,at a predetermined time rate, through a medium which absorbs, and isselectively saturated by, said major and minor components, passing theresulting gas progressively emitted by said medium through measuringmeans to derive a signal as a function of time dependent on thecomponent composition of said gas and the rate at which the componentsof said composition saturate said medium, deriving a time-function foreach said major component and the associated minor components, if any,at least one of said time-functions having at least one maximum pointdefining an axis of said time function at the instant which said maximumpoint occurs, any substantial asymmetry of said time-function about saidaxis resulting substantially only from the presence of said minorcomponents, and the time of occurrence of said last-named function beingdependent on the medium-saturation capability of said last-namedcomponents, and the area of said last-named function integrated overtime of the existence of said last-named function being dependent on therelative quantities in said specimen of said last-named components,integrating over time the areas on each side of said axis, anddetermining from said areas the relative quantity, in said specimen, ofsaid major component and comparing the area on one side of. said axiswith the area, on the other side of said axis to detect each said minorcomponent and to determine the relative quantity of each said minorcomponent.

2. The method of determining if the concentration of a gas component ina first gas specimen is different from that in a second gas specimen thesaid method comprising passing each of said specima in its turn at apredetermined time rate, through a medium which absorbs, and isselectively saturated by, said component, passing the resulting gas foreach specimen emitted by said medium through measuring means to deriverespective signals as a function of time dependent on the concentrationof said component in said specima and the rate at which said componentsaturates said medium, deriving a time function for each of saidspecima, said time function having a maximum point, the time intervalfrom the start of said function for each specimen to the instant ofoccurrence of said maximum point being herein called (I the timeinterval from the start of each said function to the center of area ofsaid last-named function being herein called (t the time duration ofeach said function being herein called (t and the height of each saidfunction being herein called h, and comparing the ratio of one of (t,,),(1, (t,;) and h to another of said last-named parameters for thefunction corresponding to one of said specima with the ratio of the samepair of parameters (t,,), (t and h for the function corresponding to theother of said specima differences between the said ratios measured forsaid first and second specima being correlated to differences inconcentration of said components in said first and second specima and/orto the presence of minor components, if any, in said first and secondspecima.

3. The method of claim 2 wherein the ratio (t lt or its reciprocal, forthe funcion corresponding to one specimen is compared with the ratio gl/p), or its reciprocal respectively, for the function corresponding tothe other specimen.

4. The method of claim 2 wherein the ratio (t lt or its reciprocal, forthe function corresponding to one specimen is compared with the ratio (t/t or its reciprocal respectively, for the function corresponding to theother specimen.

5. The method of determining the major components of the composition ofa specimen of a gas and the minor components, if any, associated witheach major component, the said method comprising passing said specimen,at a predetermined time rate, through a meduim which absorbs and isselectively saturated by, said major and minor components, passing theresulting gas progressively emitted by said medium through measuringmeans to derive a signal as a function of time dependent on thecomponent composition of said gas and the rate at which the componentsof said composition saturate said medium, deriving a time function foreach said major component and the associated minor components, if any,said time function having at least one maximum point and the time ofoccurrence of said function being dependent on the medium-saturationcapability of said last-named components and the area of said functionintegrated over time of the existence of said function being dependenton the relative quantities in said specimen of said last-namedcomponents, determining the number of points of inflexion on each sideof said maximum point of said function, comparing the number of pointsof inflexion on one side of said maximum point with the number on theother side of said maximum point, detecting the presence of saidassociated last-named minor component from a difference between thenumber of points of inflexion on one side and the number of points ofinflexion on the other side of said maximum, and integrating over timethe areas on each side of the axis of a function corresponding to amajor component of the specimen and associated minor components, if any,and by comparing the area on one side of said axis with the area on theother side of said axis determining the relative quantity of said minorcomponent in said specimen.

1. The method of determining the major components of the composition ofa specimen of a gas and the minor components, if any, associated witheach major component, the said method comprising passing said specimen,at a predetermined time rate, through a medium which absorbs, and isselectively saturated by, said major and minor components, passing theresulting gas progressively emitted by said medium through measuringmeans to derive a signal as a function of time dependent on thecomponent composition of said gas and the rate at which the componentsof said composition saturate said medium, deriving a time-function foreach said major component and the associated minor components, if any,at least one of said time-functions having at least one maximum pointdefining an axis of said time function at the instant which said maximumpoint occurs, any substantial asymmetry of said time-function about saidaxis resulting substantially only from the presence of said minorcomponents, and the time of occurrence of said last-named function beingdependent on the medium-saturation capability of said last-namedcomponents, and the area of said last-named function integrated overtime of the existence of said last-named function being dependent on therelative quantities in said specimen of said last-named components,integrating over time the areas on each side of said axis, anddetermining from said areas the relative quantity, in said specimen, ofsaid major component and comparing the area on one side of said axiswith the area, on the other side of said axis to detect each said minorcomponent and to determine the relative quantity of each said minorcomponent.
 2. The method of determining if the concentration of a gascomponent in a first gas specimen is different from that in a second gasspecimen the said method comprising passing each of said specima in itsturn at a predetermined time rate, through a medium which absorbs, andis selectively saturated by, said component, passing the resulting gasfor each specimen emitted by said medium through meaSuring means toderive respective signals as a function of time dependent on theconcentration of said component in said specima and the rate at whichsaid component saturates said medium, deriving a time function for eachof said specima, said time function having a maximum point, the timeinterval from the start of said function for each specimen to theinstant of occurrence of said maximum point being herein called (tp),the time interval from the start of each said function to the center ofarea of said last-named function being herein called (tg1), the timeduration of each said function being herein called (tB) and the heightof each said function being herein called h, and comparing the ratio ofone of (tp), (tg1), (tB) and h to another of said last-named parametersfor the function corresponding to one of said specima with the ratio ofthe same pair of parameters (tp), (tg1), (tB) and h for the functioncorresponding to the other of said specima differences between the saidratios measured for said first and second specima being correlated todifferences in concentration of said components in said first and secondspecima and/or to the presence of minor components, if any, in saidfirst and second specima.
 3. The method of claim 2 wherein the ratio(tg1/tp), or its reciprocal, for the funcion corresponding to onespecimen is compared with the ratio (tg1/tp), or its reciprocalrespectively, for the function corresponding to the other specimen. 4.The method of claim 2 wherein the ratio (tp/tB), or its reciprocal, forthe function corresponding to one specimen is compared with the ratio(tp/tB), or its reciprocal respectively, for the function correspondingto the other specimen.
 5. The method of determining the major componentsof the composition of a specimen of a gas and the minor components, ifany, associated with each major component, the said method comprisingpassing said specimen, at a predetermined time rate, through a meduimwhich absorbs and is selectively saturated by, said major and minorcomponents, passing the resulting gas progressively emitted by saidmedium through measuring means to derive a signal as a function of timedependent on the component composition of said gas and the rate at whichthe components of said composition saturate said medium, deriving a timefunction for each said major component and the associated minorcomponents, if any, said time function having at least one maximum pointand the time of occurrence of said function being dependent on themedium-saturation capability of said last-named components and the areaof said function integrated over time of the existence of said functionbeing dependent on the relative quantities in said specimen of saidlast-named components, determining the number of points of inflexion oneach side of said maximum point of said function, comparing the numberof points of inflexion on one side of said maximum point with the numberon the other side of said maximum point, detecting the presence of saidassociated last-named minor component from a difference between thenumber of points of inflexion on one side and the number of points ofinflexion on the other side of said maximum, and integrating over timethe areas on each side of the axis of a function corresponding to amajor component of the specimen and associated minor components, if any,and by comparing the area on one side of said axis with the area on theother side of said axis determining the relative quantity of said minorcomponent in said specimen.